How 18th-century nuns held clue to possible breast cancer cure

Stopping breast cancer is a real possibility, according to Oxford professor Valerie Beral. Her Million Women study follows research that began 300 years ago as Guardian health editor Sarah Boseley reports

As early as 1700, Bernardino Ramazzini, the Italian founder of occupational medicine, recognised that there was one female occupation whose members were far more likely to die from breast cancer than any other - nuns.

Evidence for the protective effect of having children and breastfeeding has accumulated in the years since. In the 1920s, British doctor Janet Lane-Claypon's pioneering epidemiological survey for the Ministry of Health demonstrated that breast cancer was linked to a woman's number of children, lactation, and age at first pregnancy and menopause.

There have been debates over which of these factors is more important, but the size of the Million Women study, led by Valerie Beral from the clinical epidemiology unit at Oxford University, has made its results fairly conclusive. Beral yesterday challenged the medical industry to turn its attention to preventing the disease.

The Million Women study found having a first baby at a young age is protective, as is late onset of puberty and early menopause. Taller and heavier women are at greater risk. But the biggest protective factors are the number of children and years of breastfeeding. A woman has a 7% decreased risk of breast cancer per birth and her risk drops by a further 4% for every year of breastfeeding.

Beral says it should be possible to develop a hormonal treatment or vaccine to give women without large families the same sort of protection.

Her study also found hormone replacement therapy (HRT) accounted for 1,000 extra breast cancers a year. Obesity in post-menopausal women is responsible for a further 4,000 and alcohol 5,000 - but few people want to take that on board, Beral says.

Cancer research has mainly focused on treatment rather than prevention. It has been successful - the British drug Tamoxifen made a significant contribution to a fall in deaths. New drugs, such as Herceptin for more difficult types of breast cancer, are becoming available. In 1989, 15,625 women died from breast cancer, but although the number of cases has climbed by 50%, deaths dropped to 12,319 by 2006. Survival rates are now far better, but the treatment is gruelling.